1. Field of the Invention
The present invention relates to a fuel supply control system for an internal combustion engine, and more particularly to a fuel pump control system which controls the fuel pump according to the flow rate of the fuel returned from the engine.
2. Description of the Prior Art
Recently, electrical fuel feed pumps for automotive vehicles having electrical drive motors have been used extensively. The feed pumps are classified mainly into rotary types and reciprocal types. Generally, these feed pumps supply fuel at a constant rate independently of the engine rotational speed and fuel consumption rate and return surplus fuel through a fuel return passageway to the fuel tank.
In such a fuel supply-return system, most of the fuel supplied to the engine is returned to the tank during low engine speed (idling) when only a small amount of fuel is consumed, so that the pump is operated at an unnecessarily high rate. Further, uncomfortably loud pump operating noises are transmitted to the driver and passengers in the car because the pump rotates at its full speed during low speed engine rotation when engine noise is low.
In order to solve these drawbacks, systems have been proposed which sense the engine speed, the vehicle speed, the engine intake pressure, changes in the pump discharge pressure and so forth to calculate the fuel consumption rate of the engine, thereby controlling the voltage or current of the pump drive electrical circuit. It is very difficult, however, to sense a fuel consumption rate corresponding to a vehicle running pattern. These systems require several sensors to detect the above operational parameters, and a complicated electrical circuit which processes the signals from the sensors. Thus these systems are very expensive.